I bought the Trekker when my first was young and it was one of the only ones available of its kind. I found it too bulky and it was hard to adjust because the position it needed was right between one of the clasps.
The Trekker doesn't put the baby in the natural knees above bum position that is recommended for safe baby wearing and instead the knees are low and the baby is suspended by the crotch and the head isn't supported at all when baby falls asleep.
I also didn't like that the facing out on back position that they advocate. The baby's back is rounded against the parents back in a very awkward position.